1. Field of the Invention
This invention relates to flywheel energy storage systems, to integration of advanced-technology fiber-reinforced composite thick-ring flywheels, low-cost continuous-filament unbonded steel wire and other filament flywheels and mounting hub designs, with ultra-compact and in some cases low-cost conventional motor/generators and digital signal processing-based electronic controller systems, fail-safe vacuum enclosures, emergency energy-dump and containment systems and ball, roller and sleeve bearings having solid lubricants, all of which can operate reliably for many years without maintenance. This invention also relates to the use of the gyroscopic moment generated by such flywheel for orienting the load of a suspended device in the manner described in U.S. Pat. No. 5,632,222, in addition to, or instead of, energy storage.
2. Description of the Prior Art
Storing energy as kinetic energy in a rotating flywheel is known. However, despite recent improvements in fiber-reinforced composites, continuous-filament-wound ring designs, electronic controls, and bearing lubrication and vibration-control technology, flywheel energy systems have still been only potentially competitive with alternative energy storage devices such as chemical batteries and ultra-capacitors.
Conventional flywheel materials are limited in their energy storage capacity by their centrifugal burst strength at high rotating speeds.
Motor/generators and controls typically used with flywheels are too bulky and cannot run at the high speeds required for a compact flywheel energy storage system to fit the volume constraints of automotive and other vehicular applications.
Application of lower energy density flywheel energy storage systems for stationary utility load-leveling applications has not been successful due in part to lack of proven designs for low-cost continuous-filament ring materials.
The transverse-flux permanent magnet motor provides high power densities with high efficiency and is believed to have been first described by Dr. H. Weh in a paper published in 1988 entitled “New Permanent Magnet Excited Synchronous Machine With High Efficiency at Low Speeds” as a means to obtain high power densities with high efficiencies to reduce weight, cost, energy losses and maintenance.
Conventional commercial brushless DC motors use Hall effect, i.e. magnetically switched, non-contacting sensors to sense rotor position. A signal is provided to an inverter to commutate to the next phase in sequence when the root magnet axis reaches a predetermined position. In this way motor windings are energized so as to maximize the amount of torque output for the motor at any given speed. However, known Hall-effect systems are complex, awkward and difficult to manufacture, install and align, limiting their use in high-speed machines where brushless characteristics are a distinct advantage.
Conventional high-speed bearings require a supply of air-oil mist, circulating lubricating oil or periodic replenishment of grease to provide adequate lubrication between the moving surfaces, so friction does not cause the bearings to overheat and self-destruct during operation.
In high-speed flywheel energy storage systems, conventional bearings do not have sufficient life in the vacuum environment required to minimize windage losses and composite flywheel ring overheating. Thus, some flywheel systems rely on active magnetic bearings. Even magnetic bearings, however, require auxiliary ball or roller bearings to support the rotor in the event either of an inadvertent loss of power to the magnetic bearings or high gyroscopic maneuvering or impact loads that exceed the load capability of the magnetic bearings.
Lubricating greases and the ultra-low volatility synthetic lubricating oils required in the high vacuum of such systems with low cost ball bearings do not have the additive response of synthetic hydrocarbons or conventional petroleum-based oils, so that they have unacceptably short boundary lubricating ability and bearing life. In this regard see the paper by Mahncke and Schwartz entitled “Grease Lubrication of Rolling Bearings in Spacecraft” published in ASLE Transactions, Vol. 17, No. 3, Pgs. 172–181.
High rotating speeds result in so much centrifugal expansion of flywheel-rings that special provisions are required to mount such rings on bearing-supported rotors with the motor/generator rotor. The mounting system in U.S. Pat. No. 4,860,611 provides a mounting hub design suitable for use at substantially high speeds, but even higher speeds are desirable. Hence, further improvements in mounting designs are needed.
Adequately reliable solid-lubricated, high-speed bearing systems for use in especially high vacuum environments are not known. The bearing industry markets several types of dry bearing materials based on such molybdenum disulfide, graphite, Teflon and other plastics used as solid lubricants. Woven glass fiber-reinforced Teflon bearings are fabricated by bonding a stiff metal backing to a thin composite layer of soft lubricating Teflon, reinforced with a hard glass fabric. A very thin film of Teflon lubricates the glass fibers with a minimum of deflection, plastic flow and wear. In such known solid-lubricated bearing applications, sporadic catastrophic bearing failures occur.
Self-contained greased-for-life bearings have limited high-speed capabilities and require frequent re-lubrication.
In high-speed rotors operating above critical speed, the bearings are usually lubricated with circulating oil. In the case of high-speed ball or roller bearings, this lubricating oil is often circulated through an annular space in the housing that separates the non-rotating bearing ring from the main housing of the machine, so that the radial load on the bearing squeezes this oil film. Vibrations of the rotor are dampened by viscous flow of the oil film as the rotor passes through critical speeds while accelerating and decelerating from its operating speed.
In currently available rotating machinery it is common to use “squeeze-film” dampers and precision balanced rotors to control vibration response and bearing loads in high speed rotating machinery. Unfortunately, squeeze-film dampers have their own instabilities due to oil whirl and oil whip and often induce instabilities in such high speed machinery. Additionally, squeeze-film damper design is an ill-defined art. Furthermore, squeeze-film dampers do not provide high damping ratios. Hence, high vibrational bearing loads and system instabilities often result when squeeze-film dampers are utilized.